A novel retractable laparoscopic device for mapping gastrointestinal slow wave propagation patterns

In vivo experimental validation of detection of gastric slow waves using a flexible multichannel electrogastrography sensor linear array

Background

Cutaneous electrogastrography (EGG) is a non-invasive technique that detects gastric bioelectrical slow waves, which in part govern the motility of the stomach. Changes in gastric slow waves have been associated with a number of functional gastric disorders, but to date accurate detection from the body-surface has been limited due to the low signal-to-noise ratio. The main aim of this study was to develop a flexible active-electrode EGG array. Methods: Two Texas Instruments CMOS operational amplifiers: OPA2325 and TLC272BID, were benchtop tested and embedded in a flexible linear array of EGG electrodes, which contained four recording electrodes at 20-mm intervals. The cutaneous EGG arrays were validated in ten weaner pigs using simultaneous body-surface and serosal recordings, using the Cyton biosensing board and ActiveTwo acquisition systems. The serosal recordings were taken using a passive electrode array via surgical access to the stomach. Signals were filtered and compared in terms of frequency, amplitude, and phase-shift based on the classification of propagation direction from the serosal recordings. Results: The data were compared over 709 cycles of slow waves, with both active cutaneous EGG arrays demonstrating comparable performance. There was an agreement between frequencies of the cutaneous EGG and serosal recordings (3.01 ± 0.03 vs 3.03 ± 0.05 cycles per minute; p = 0.75). The cutaneous EGG also demonstrated a reduction in amplitude during abnormal propagation of gastric slow waves (310 ± 50 µV vs 277 ± 9 µV; p < 0.01), while no change in phase-shift was observed (1.28 ± 0.09 s vs 1.40 ± 0.10 s; p = 0.36). Conclusion: A sparse linear cutaneous EGG array was capable of reliably detecting abnormalities of gastric slow waves. For more accurate characterization of gastric slow waves, a two-dimensional body-surface array will be required.

Effects of anatomical variations of the stomach on body-surface gastric mapping investigated using a large population-based multiscale simulation approach

The contractions of the stomach are governed by bioelectrical slow waves that can be detected non-invasively from the body-surface. Diagnosis of gastric motility disorders remains challenging due to the limited information provided by symptoms and tests, including standard electrogastrography (EGG). Body-surface gastric mapping (BSGM) is a novel technique that measures the resultant body-surface potentials using an array of multiple cutaneous electrodes. However, there is no established protocol to guide the placement of the mapping array and to account for the effects of biodiversity on the interpretation of gastric BSGM data. This study aims to quantify the effect of anatomical variation of the stomach on body surface potentials. To this end, 93 subject specific models of the stomach and torso were developed. Anatomical models were developed based on data obtained from the Cancer Imaging Archive. For each subject a set of points were created to model general anatomy the stomach and the torso, using a finite element mesh. A bidomain model was used to simulate the gastric slow waves in the antegrade wave (AW) direction and formation of colliding waves (CW). The resultant dipole was calculated, and a forward modeling approach was employed to simulate body-surface potentials. Simulated data were sampled from a 55 array of electrodes from the body-surface and compared between AW and CW cases. Anatomical parameters such as the Euclidean distance from the xiphoid process (8.6 2.2 cm), orientation relative to the axial plane (195 20.0) were quantified. Electrophysiological simulations of AW and CW were both correlated to specific metrics derived from BSGM signals. In general, the maximum amplitude () and orientation () of the signals provided consistent separation of AW and CW. The findings of this study will aid gastric BSGM electrode array design and placement protocol in clinical practices.

Body surface mapping of the stomach: New directions for clinically evaluating gastric electrical activity

BACKGROUND

Gastric motility disorders, which include both functional and organic etiologies, are highly prevalent. However, there remains a critical lack of objective biomarkers to guide efficient diagnostics and personalized therapies. Bioelectrical activity plays a fundamental role in coordinating gastric function and has been investigated as a contributing mechanism to gastric dysmotility and sensory dysfunction for a century. However, conventional electrogastrography (EGG) has not achieved common clinical adoption due to its perceived limited diagnostic capability and inability to impact clinical care. The last decade has seen the emergence of novel high-resolution methods for invasively mapping human gastric electrical activity in health and disease, providing important new insights into gastric physiology. The limitations of EGG have also now become clearer, including the finding that slow-wave frequency alone is not a reliable discriminator of gastric dysrhythmia, shifting focus instead toward altered spatial patterns. Recently, advances in bioinstrumentation, signal processing, and computational modeling have aligned to allow non-invasive body surface mapping of the stomach to detect spatiotemporal gastric dysrhythmias. The clinical relevance of this emerging strategy to improve diagnostics now awaits determination.

PURPOSE

This review evaluates these recent advances in clinical gastric electrophysiology, together with promising emerging data suggesting that novel gastric electrical signatures recorded at the body surface (termed "body surface mapping") may correlate with symptoms. Further technological progress and validation data are now awaited to determine whether these advances will deliver on the promise of clinical gastric electrophysiology diagnostics.

Electroceuticals in the Gastrointestinal Tract

The field of electroceuticals has attracted considerable attention over the past few decades as a novel therapeutic modality. The gastrointestinal (GI) tract (GIT) holds significant potential as a target for electroceuticals as the intersection of neural, endocrine, and immune systems. We review recent developments in electrical stimulation of various portions of the GIT (including esophagus, stomach, and small and large intestine) and nerves projecting to the GIT and supportive organs. This has been tested with varying degrees of success for several dysmotility, inflammatory, hormonal, and neurologic disorders. We outline a vision for the future of GI electroceuticals, building on advances in mechanistic understanding of GI physiology coupled with novel ingestible technologies. The next wave of electroceutical therapies will be minimally invasive and more targeted than current approaches, making them an indispensable tool in the clinical armamentarium.

Bioelectrical Signals for the Diagnosis and Therapy of Functional Gastrointestinal Disorders

Coordinated contractions and motility patterns unique to each gastrointestinal organ facilitate the digestive process. These motor activities are coordinated by bioelectrical events, sensory and motor nerves, and hormones. The motility problems in the gastrointestinal tract known as functional gastrointestinal disorders (FGIDs) are generally caused by impaired neuromuscular activity and are highly prevalent. Their diagnosis is challenging as symptoms are often vague and difficult to localize. Therefore, the underlying pathophysiological factors remain unknown. However, there is an increasing level of research and clinical evidence suggesting a link between FGIDs and altered bioelectrical activity. In addition, electroceuticals (bioelectrical therapies to treat diseases) have recently gained significant interest. This paper gives an overview of bioelectrical signatures of gastrointestinal organs with normal and/or impaired motility patterns and bioelectrical therapies that have been developed for treating FGIDs. The existing research evidence suggests that bioelectrical activities could potentially help to identify the diverse etiologies of FGIDs and overcome the drawbacks of the current clinically adapted methods. Moreover, electroceuticals could potentially be effective in the treatment of FGIDs and replace the limited existing conventional therapies which often attempt to treat the symptoms rather than the underlying condition.

Bioelectronics for mapping gut activity

Gastric peristalsis is initiated and coordinated by an underlying bioelectrical activity, termed slow waves. High-resolution (HR) mapping of the slow waves has become a fundamental tool for accurately defining electrophysiological properties in gastroenterology, including dysrhythmias in gastric disorders such as gastroparesis and functional dyspepsia. Currently, HR mapping is achieved via acquisition of slow waves taken directly from the serosa of fasted subjects undergoing invasive abdominal surgery. Recently, a minimally invasive retractable catheter and electrode has been developed for HR mapping that can only be used in short-term studies in subjects undergoing laparoscopy. Noninvasive mapping has also emerged from multichannel cutaneous electrogastrography; however, it lacks sufficient resolution and is prone to artifacts. Bioelectronics that can map slow waves in conscious subjects, postprandially and long-term, are in high demand. Due to the low signal-to-noise ratio of cutaneous electrogastrography, electrodes for HR mapping of gut activity have to acquire slow waves directly from the gut; hence, development of novel device implantation methods has inevitably accompanied development of the devices themselves. Initial efforts that have paved the way toward achieving these goals have included development of miniature wireless systems with a limited number of acquisition channels using commercially available off-the-shelf electronic components, flexible HR electrodes, and endoscopic methods for minimally invasive device implantation. To further increase the spatial resolution of HR mapping, and to minimize the size and power consumption of the implant for long-term studies, application-specific integrated circuitry, wireless power transfer, and stretchable electronics technologies have had to be integrated into a single system.

Bimetallic Pt,Ir-containing coatings formed by MOCVD for medical applications

Biocompatible Pt_xIr_(1-x) layers combining high mechanical strength of the iridium component and outstanding corrosion resistance of the platinum component providing reversible charge transfer reactions in the living tissue are one of the important materials required for implantable medical electrodes. The modern trend to complicate the shape and reduce the electrode dimensions includes the challenge to develop precise methods to obtain such bimetallic coatings with enhanced surface area and advanced electrochemical characteristics. Herein, Pt_xIr_(1-x) coatings were firstly obtained on cathode and anode pole tips of endocardial electrodes for pacemakers using chemical vapor deposition technique. To deposit Pt_xIr_(1-x) coatings with a wide range of metal ratios (x = 0.5-0.9) the combination of acetylacetonate-based volatile precursors with compatible thermal characteristics was used for the first time. The expected metal ratio in the coatings was regulated by a partial pressure of the precursor vapors in the reaction zone and was in the good agreement with its real value measured by various methods, including energy-dispersive and wavelength dispersive spectroscopy, X-ray photoelectron spectroscopy. According to the X-ray powder diffraction analysis, Pt_xIr_(1-x) coatings consisted of fcc-Pt_xIr_(1-x) solid solution phases. The microscopy data confirmed the formation of Pt_xIr_1-x coatings with the enhanced surface areas. The effect of electrochemical activation on the surface composition and morphology of the samples was studied. The electrochemical characteristics of samples were estimated from cyclic voltammetry and electrochemical impedance spectroscopy data. The charge storage capacity (CSC) values of activated samples were in the range of 19-108 mCcm^-2 (phosphate buffer saline solution, 100 mV/s).

Methods for High-Resolution Electrical Mapping in the Gastrointestinal Tract

Over the last two decades, high-resolution (HR) mapping has emerged as a powerful technique to study normal and abnormal bioelectrical events in the gastrointestinal (GI) tract. This technique, adapted from cardiology, involves the use of dense arrays of electrodes to track bioelectrical sequences in fine spatiotemporal detail. HR mapping has now been applied in many significant GI experimental studies informing and clarifying both normal physiology and arrhythmic behaviors in disease states. This review provides a comprehensive and critical analysis of current methodologies for HR electrical mapping in the GI tract, including extracellular measurement principles, electrode design and mapping devices, signal processing and visualization techniques, and translational research strategies. The scope of the review encompasses the broad application of GI HR methods from in vitro tissue studies to in vivo experimental studies, including in humans. Controversies and future directions for GI mapping methodologies are addressed, including emerging opportunities to better inform diagnostics and care in patients with functional gut disorders of diverse etiologies.

Patterns of Abnormal Gastric Pacemaking After Sleeve Gastrectomy Defined by Laparoscopic High-Resolution Electrical Mapping

BACKGROUND

Laparoscopic sleeve gastrectomy (LSG) is increasingly being applied to treat obesity. LSG includes excision of the normal gastric pacemaker, which could induce electrical dysrhythmias impacting on post-operative symptoms and recovery, but these implications have not been adequately investigated. This study aimed to define the effects of LSG on gastric slow-wave pacemaking using laparoscopic high-resolution (HR) electrical mapping.

METHODS

Laparoscopic HR mapping was performed before and after LSG using flexible printed circuit arrays (64-96 electrodes; 8-12 cm²; n = 8 patients) deployed through a 12 mm trocar and positioned on the gastric serosa. An additional patient with chronic reflux, nausea, and dysmotility 6 months after LSG also underwent gastric mapping while undergoing conversion to gastric bypass. Slow-wave activity was quantified by propagation pattern, frequency, velocity, and amplitude.

RESULTS

Baseline activity showed exclusively normal propagation. Acutely after LSG, all patients developed either a distal unifocal ectopic pacemaker with retrograde propagation (50%) or bioelectrical quiescence (50%). Propagation velocity was abnormally rapid after LSG (12.5 ± 0.8 vs baseline 3.8 ± 0.8 mm s^-1; p = 0.01), whereas frequency and amplitude were unchanged (2.7 ± 0.3 vs 2.8 ± 0.3 cpm, p = 0.7; 1.7 ± 0.2 vs 1.6 ± 0.6 mV, p = 0.7). In the patient with chronic dysmotility after LSG, mapping also revealed a stable antral ectopic pacemaker with retrograde rapid propagation (12.6 ± 4.8 mm s^-1).

CONCLUSION

Resection of the gastric pacemaker during LSG acutely resulted in aberrant distal ectopic pacemaking or bioelectrical quiescence. Ectopic pacemaking can persist long after LSG, inducing chronic dysmotility. The clinical and therapeutic significance of these findings now require further investigation.

Improved Visualization of Gastrointestinal Slow Wave Propagation Using a Novel Wavefront-Orientation Interpolation Technique

OBJECTIVE

High-resolution mapping of gastrointestinal (GI) slow waves is a valuable technique for research and clinical applications. Interpretation of high-resolution GI mapping data relies on animations of slow wave propagation, but current methods remain as rudimentary, pixelated electrode activation animations. This study aimed to develop improved methods of visualizing high-resolution slow wave recordings that increases ease of interpretation.

METHODS

The novel method of "wavefront-orientation" interpolation was created to account for the planar movement of the slow wave wavefront, negate any need for distance calculations, remain robust in atypical wavefronts (i.e., dysrhythmias), and produce an appropriate interpolation boundary. The wavefront-orientation method determines the orthogonal wavefront direction and calculates interpolated values as the mean slow wave activation-time (AT) of the pair of linearly adjacent electrodes along that direction. Stairstep upsampling increased smoothness and clarity.

RESULTS

Animation accuracy of 17 human high-resolution slow wave recordings (64-256 electrodes) was verified by visual comparison to the prior method showing a clear improvement in wave smoothness that enabled more accurate interpretation of propagation, as confirmed by an assessment of clinical applicability performed by eight GI clinicians. Quantitatively, the new method produced accurate interpolation values compared to experimental data (mean difference 0.02 ± 0.05 s) and was accurate when applied solely to dysrhythmic data (0.02 ± 0.06 s), both within the error in manual AT marking (mean 0.2 s). Mean interpolation processing time was 6.0 s per wave.

CONCLUSION AND SIGNIFICANCE

These novel methods provide a validated visualization platform that will improve analysis of high-resolution GI mapping in research and clinical translation.

Relationships between gastric slow wave frequency, velocity, and extracellular amplitude studied by a joint experimental-theoretical approach

BACKGROUND

Gastric slow wave dysrhythmias are accompanied by deviations in frequency, velocity, and extracellular amplitude, but the inherent association between these parameters in normal activity still requires clarification. This study quantified these associations using a joint experimental-theoretical approach.

METHODS

Gastric pacing was conducted in pigs with simultaneous high-resolution slow wave mapping (32-256 electrodes; 4-7.6 mm spacing). Relationships between period, velocity, and amplitude were quantified and correlated for each wavefront. Human data from two existing mapping control cohorts were analyzed to extract and correlate these same parameters. A validated biophysically based ICC model was also applied in silico to quantify velocity-period relationships during entrainment simulations and velocity-amplitude relationships from membrane potential equations.

KEY RESULTS

Porcine pacing studies identified positive correlations for velocity-period (0.13 mm s^-1 per 1 s, r² =.63, P<.001) and amplitude-velocity (74 μV per 1 mm s^-1 , r² =.21, P=.002). In humans, positive correlations were also quantified for velocity-period (corpus: 0.11 mm s^-1 per 1 s, r² =.16, P<.001; antrum: 0.23 mm s^-1 per 1 s, r² =.55; P<.001), and amplitude-velocity (94 μV per 1 mm s^-1 , r² =.56; P<.001). Entrainment simulations matched the experimental velocity-period relationships and demonstrated dependence on the slow wave recovery phase. Simulated membrane potential relationships were close to these experimental results (100 μV per 1 mm s^-1 ).

CONCLUSIONS AND INFERENCES

These data quantify the relationships between slow wave frequency, velocity, and extracellular amplitude. The results from both human and porcine studies were in keeping with biophysical models, demonstrating concordance with ICC biophysics. These relationships are important in the regulation of gastric motility and will help to guide interpretations of dysrhythmias.